add_filter ('bp_ajax_querystring', 'modify_members_loop', 20, 2);
function modify_members_loop ($qs=false, $object=false)
{
    global $wpdb;
    if ($object != 'members')  return $qs;

    // figure out if the logged-in user is male or female
    $gender = xprofile_get_field_data (3, bp_loggedin_user_id ());

    if ($gender == 'Sugardaddy')
        $query = "SELECT user_id FROM {$wpdb->prefix}bp_xprofile_data WHERE field_id = 3 AND value = 'Sugarbaby'";
    else
        $query = "SELECT user_id FROM {$wpdb->prefix}bp_xprofile_data WHERE field_id = 3 AND value = 'Sugardaddy'";

    $custom_ids = $wpdb->get_col ($query);

    $args = wp_parse_args ($qs);
    $args['include'] = implode (',', $custom_ids);
    $qs = build_query ($args);

    return $qs;
}